Abstract:

Carbonate fractured-vuggy reservoirs in the Middle-Lower Ordovician of the Tarim Basin are strongly controlled by deep strike-slip faults. Their pronounced heterogeneity has become a key challenge to the efficient exploitation of ultra-deep oil and gas resources. In this study, a representative strike-slip fault within a carbonate outcrop on the northwestern margin of the basin was selected as the research target. By integrating multiple analytical approaches, including field structural measurements, petrographic thin-section observations, high-pressure mercury intrusion porosimetry, and rock physics experiments, the study systematically characterizes the multi-scale heterogeneity of fault-controlled carbonate fractured-vuggy reservoirs and identifies their dominant controlling factors. The development patterns of high-quality reservoir zones are also summarized. At the macro scale, fracture distribution along the fault strike is highly uneven, with the overlap segments exhibiting the highest fracture densities. Within these segments, the boundary fault zones are characterized by small breccias with high roundness, indicating strong interconnectivity. Along the dip direction, fault core zones are distinguished by abundant large fractures and vugs with only minor vein filling. These zones have porosities approximately 4~6 times those of the damage zones and compressive strengths only 25%~50% as high, making them prime sites for high-quality reservoir development. Vertically, zones of high porosity and low strength alternate with sealing layers, resulting in a discrete vertical distribution of high-quality reservoirs. At the micro scale, fault cores exhibit diverse pore types, including intracrystalline pores, intercrystalline pores, semi-filled microfractures, and microvugs. In addition, they display high surface porosity, large pore aspect ratios, numerous interconnected pore nodes, and well-developed throat channels, which together contribute to their significantly higher permeability compared with the damage zones. On this basis, the Lorenz curve method is combined with the entropy weight method, which is applied for the first time to evaluate the heterogeneity of fault-controlled carbonate fractured-vuggy reservoirs. The evaluation results indicate that these reservoirs exhibit overall strong heterogeneity, with the micro scale showing a higher degree than the macro scale. This heterogeneity is primarily governed by the coupling of fault structures and diagenetic fluid-driven dissolution-precipitation processes. Integrating these findings, three types of “sweet spot” zones are identified within the fault-controlled reservoirs: boundary fault zones in the overlap segments along the fault strike, fault core zones along the dip, and dolomitic limestone intervals in the vertical sequence. This study fills a gap in understanding the heterogeneity of fault-controlled carbonate fractured-vuggy reservoirs and provides theoretical support for improving the recovery efficiency of ultra-deep oil and gas resources.

Key words: strike-slip fault, carbonate rock, fracture-vuggy reservoir, reservoir heterogeneity, Tarim Basin

摘要：

塔里木盆地中-下奥陶统碳酸盐岩缝洞型储层受深部走滑断裂构造控制，显著的非均质性已成为制约超深层油气藏高效开发的关键因素。本文以盆地西北缘碳酸盐岩露头区一条典型走滑断层为研究对象，综合运用野外构造实测、岩石薄片观察、高压压汞与岩石物理实验等多种手段，系统揭示了断控碳酸盐岩缝洞型储层的多尺度非均质性特征及其主控因素，归纳总结了优质储层的发育规律。在宏观尺度上，沿断层走向的裂缝分布极不均匀，其中，叠接段裂缝最密。在叠接段内部，边界断层区域的角砾小、磨圆度高，连通性强。沿倾向方向，断层核区域裂缝与溶洞发育，脉体充填少，储层物性是破碎带的4~6倍，抗压强度仅为其25%~50%，为优质储层发育部位。垂向上，高物性、低强度区与隔挡层交互分布，优质储层呈离散状分布。在微观尺度上，断层核区域发育晶内孔、晶间孔、半充填微裂缝及微孔洞，孔隙类型多样。同时该区域面孔率高，孔隙纵横比大，连通节点多，孔喉通道发育，渗透率明显优于破碎带。在此基础上，本文首次将洛伦兹曲线法与熵权法相结合，应用于断控碳酸盐岩缝洞型储层的非均质性评价。评价结果表明该类储层整体表现为强非均质性特征，且微观尺度非均质性显著高于宏观尺度。其非均质性的形成主要受断层结构与成岩流体溶蚀-沉淀作用两个因素耦合控制。综合以上认识，总结出断控储层的3类“甜点”发育部位为沿断层走向的叠接段边界断层带区域，沿倾向方向的断层核区域以及垂向上的白云质灰岩段。研究成果弥补了断控碳酸盐岩缝洞型储层非均质性研究的不足，为提升超深层剩余油开发效率提供了理论支撑。

关键词: 走滑断层, 碳酸盐岩, 缝洞型储层, 储层非均质性, 塔里木盆地

CLC Number: 

• P618.13

• TE122.2